Dilation system

ABSTRACT

A dilation system for accessing a surgical target site to perform surgical procedures. In one version, the dilation system includes a plurality of open sided dilators having non-circular cross sections and configured to slidably and non-rotationally engage with one another in a sequential manner. In another version, the dilation system includes an expandable dilator movable from a closed condition to an expanded condition.

BACKGROUND OF THE PRESENTLY DISCLOSED INVENTIVE CONCEPTS

1. Field of the Presently Disclosed Inventive Concepts

The inventive concepts disclosed and claimed herein relate to systemsand methods for performing surgical procedures and, more particularly,but not by way of limitation, to systems and methods for accessing asurgical target site to perform surgical procedures.

2. Brief Description of Related Art

The present state of the art, when referencing a lateral surgical accessapproach, typically consists of using the following surgicalinstruments: neuromonitoring probe, dilators, and a retractor. Once anoperative level is identified and an incision is created, dilators areused to create a surgical access site which is often followed by the useof a retractor or other specialized tools to create a surgical accesscorridor.

During a lateral approach to a patient's spine, a psoas muscle, which islocated on either side of the spine, is separated in order to access thespine and, in particular, an intervertebral disc space or one or morevertebral bodies within a patient's spinal column. It is desirable toavoid neural elements or nerves of the lumbar plexus that lie within thepsoas muscle during such procedures. The anterior third of the psoasmuscle is typically considered a safe zone for muscle separation.

The neural elements or nerves of the psoas muscle may be mapped using astimulating probe. In this manner, the most posterior neural or nervefree area of the psoas muscle may be located and identified. Thestimulating probe may then be inserted through the psoas muscle via themost posterior neural or nerve free tissue area or through nearly anyother region that is free of neural elements or nerves and toward thespine or into the intervertebral disc space in order to initiate safetissue separation of the psoas muscle. Dilators are next placed over theprobe to create and enlarge a surgical access site. Following the use ofdilators, a retractor or other specialized tools are used to furtherenlarge the surgical access corridor.

Concentric dilators separate the muscle radially, and as such, dilatetissue on all both sides of the stimulating probe in a uniform fashion.This in turn may impinge on neural elements or nerves located outside ofthe safe zone. Directional dilators have been suggested to overcome theproblems associated with concentric dilators. While directional dilationsystems are effective have avoiding known neural elements, they arelimited in their ability to continuously monitor nerve proximity and tocreate a surgical access site of a desired shape while at the same timereducing the amount of tissue damage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially exploded, perspective view of a dilation systemconstructed in accordance with the inventive concepts disclosed hereinhaving three dilators and three electrode assemblies.

FIG. 2 is an elevational view of the dilation system of FIG. 1.

FIG. 3 is an elevational view of the dilation system of FIG. 2 shownrotated 90 degrees.

FIG. 4A is a top plan view of the dilation system.

FIG. 4B is a bottom plan view of the dilation system.

FIG. 4C is an elevational view of a first dilator.

FIG. 4D is a top plan view of the first dilator.

FIG. 4E is a top plan view of another embodiment of a first dilator.

FIGS. 5A is an elevational view of the dilators shown without theelectrode assemblies and shown assembled in a concentric arrangement.

FIG. 5B is a bottom plan view of the dilators shown without theelectrode assemblies and shown assembled in a concentric arrangement.

FIG. 6 is a bottom plan view of the dilators without the electrodeassemblies and shown arranged in an eccentric arrangement.

FIG. 7 is an elevational view of another embodiment of a dilation systemconstructed in accordance with the inventive concepts disclosed hereinhaving three dilators.

FIG. 8 is a bottom plan view of the dilation system of FIG. 7.

FIG. 9 is a top plan view of the dilation system of FIG. 7 shown in aconcentric arrangement.

FIG. 10 is a top plan view of the dilation system of FIG. 7 shown in aneccentric arrangement.

FIG. 11A is an elevational view of an exemplary first dilator of thedilation system of FIG. 7.

FIG. 11 B is a top plan view of the first dilator.

FIG. 12A is an elevational view of an exemplary second dilator of thedilation system of FIG. 7.

FIG. 12B is a top plan view of the second dilator.

FIG. 13A is an elevational view of an exemplary third dilator of thedilation system of FIG. 7.

FIG. 13B is an elevational view of the third dilator of FIG. 13A shownrotated 90 degrees.

FIG. 13C is a top plan view of the third dilator.

FIG. 14 is a perspective view of another embodiment of a dilation systemconstructed in accordance with the inventive concepts disclosed herein.

FIG. 15A is a perspective view of an exemplary first dilator shown beinginserted over a stimulating probe.

FIG. 15B is a perspective view of an exemplary second dilator beinginserted over the first dilator.

FIG. 15C is a perspective view of an exemplary third dilator beinginserted over the first dilator.

FIG. 16A is a front elevational view of the first dilator of thedilation system of FIG. 14.

FIG. 16B is a side elevatonal view of the first dilator.

FIG. 16C is a rear elevational view of the first dilator.

FIG. 16D is a sectional view taken along line 16D-16D of FIG. 16C.

FIG. 17 is a sectional view taken along line 17-17 of FIG. FIG. 16B.

FIG. 18 is top end view of the first dilator.

FIG. 19 is a front elevational view of an exemplary second dilator ofthe dilation system of FIG. 14.

FIG. 20A is a sectional view taken along line 20A-20A of FIG. 19.

FIG. 20B is a sectional view taken along line 20B-20B of FIG. 19.

FIG. 21 is a front elevational view of an exemplary third dilator of thedilation system of FIG. 14.

FIG. 22A is a sectional view taken along line 22A-22A of FIG. 21.

FIG. 22B is a sectional view taken along line 22B-22B of FIG. 21.

FIG. 23A is a perspective view of an exemplary first dilator of anotherembodiment of a dilation system.

FIG. 23B is a perspective view illustration an exemplary second dilatorconnected to the first dilator.

FIG. 23C is a sectional view of the first and second dilator shown incombination with a retractor assembly.

FIG. 24A is a perspective view of another embodiment of a dilationsystem constructed in accordance with the inventive concepts disclosedherein shown in a closed condition.

FIG. 24B is a perspective view of the dilation system of FIG. 24A shownin an expanded condition.

FIG. 25 is a sectional view taken along line 25-25 of FIG. 24B.

FIG. 26 is an exploded, perspective view of a link assembly.

FIG. 27A is an exploded, perspective view of a drive rod shown detachedfrom the link assembly.

FIG. 27B is a perspective view of the drive shaft shown attached to thelink assembly.

FIG. 28A is a perspective view of the dilation system of FIG. 14illustrated in the closed condition provided with an expandable sheath.

FIG. 28B is a perspective view of the dilation system of FIG. 28A shownin the expanded condition.

FIG. 29 is a perspective view of another embodiment of a dilation systemconstructed in accordance with the inventive concepts disclosed hereinshown in a closed condition.

FIG. 30 is a perspective view of the dilation system of FIG. 28 shown inan expanded condition.

FIG. 31 is a perspective view of the dilation system of FIG. 28 shown inthe expanded condition with a secondary expander shown inserted therein.

FIG. 32 is a perspective view of an expander.

FIG. 33 is a perspective view of the secondary expander.

FIG. 34 is a perspective view of another embodiment of a dilation systemconstructed in accordance with the inventive concepts disclosed herein.

FIG. 35 is a perspective view of the dilation system of FIG. 34 shownprovided with an expandable sheath.

FIG. 36A is an elevational view of another embodiment of a dilationsystem constructed in accordance with the inventive concepts disclosedherein.

FIG. 36B is a top end view of the dilation system of FIG. 36A.

FIG. 37A is an elevational view of the dilation system of FIG. 36A shownwith a first expansion member.

FIG. 37B is a top end view of the dilation system of FIG. 37A.

FIG. 38A is an elevational view of the dilation system of FIG. 37A shownwith a second expansion member.

FIG. 38B is a top end view of the dilation system of FIG. 38A.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Before explaining at least one embodiment of the presently disclosed andclaimed inventive concepts in detail, it is to be understood that thepresently disclosed and claimed inventive concepts is not limited in itsapplication to the details of construction, experiments, exemplary data,and/or the arrangement of the components set forth in the followingdescription or illustrated in the drawings. The presently disclosed andclaimed inventive concepts are capable of other embodiments or of beingpracticed or carried out in various ways. Also, it is to be understoodthat the phraseology and terminology employed herein is for purpose ofdescription and should not be regarded as limiting.

Certain exemplary embodiments of the invention will now be describedwith reference to the drawings. In general, such embodiments relate todilation systems for accessing a patient's spinal column.

As generally understood by one of ordinary skill in the art, thedilation systems will be described in connection with accessing thespine to perform a surgical procedure, but the dilation systems willfind use not only in orthopedic surgery, but in other surgicalprocedures in which a surgeon wishes to gain access to an internalcavity by cutting the skin and going through the body wall in order tokeep the incision spread apart so that surgical instruments can beinserted. For example, the dilation systems may be used for anteriorlyor posteriorly accessing the spine, for accessing the thoracic orcervical region of the spine, or for accessing nearly any other part ofthe body.

Referring to FIGS. 1-6, a dilation system 10 is illustrated. Thedilation system 10 includes a plurality of sequential dilators 12, 14,and 16, and a plurality of electrode assemblies 18 and 20. Thesequential dilation system 10 may include more or less dilators such as,for example, one, two four, etc. The dilation system 10 is adapted to beused in combination with a monitoring K-wire or stimulating probe (notshown) known for transmitting an electrical pulse.

Referring to FIGS. 4C-4E, 5A, and 5B, the first dilator 12 is a tubularmember having an outer surface 32, a proximal end 33, a distal end 34and a bore 35 extending from the proximal end 33 to the distal end 34.The first dilator is illustrated as having a substantially egg shapedtransverse cross section whereby the first dilator 12 is provided with alobe 36. The bore 35 is offset from the longitudinal axis of the firstdilator 12 away from lobe 36. The bore 35 is sized to receive astimulating probe (not shown). Alternatively, the first dilator 12 maybe provided with a channel 38 formed near the tip of the lobe andextending the length of the first dilator 12 (FIG. 6), or the firstdilator 12 may have an open side 37 opposite the lobe 36 (FIG. 4E).

In use, the first bore 35 removably receives the stimulating probe in anassembled configuration (e.g., when the stimulating probe is slidablyreceived within the first bore 35 of the first directional dilator 12)so that a surgeon can stimulate the first dilator 12. The axis of thestimulating probe may be coaxial with the axis of the bore 35 of thefirst dilator 12 in the assembled configuration.

With reference to FIGS. 5A and 5B, the second dilator 14 ischaracterized as being an open sided tubular structure that has an outersurface 42, a proximal end 43, a distal end 44, and a bore 45 extendingfrom the proximal end 43 to the distal end 44. The second dilator 14 isillustrated as having a substantially oval shaped transverse crosssection. The bore 45 is offset from the longitudinal axis of the seconddilator 14 toward the open side of the second dilator 14. The bore 45 isshaped to slidingly receive the first dilator 12 so that the tip of thelobe 36 of the first dilator 12 is received in the open side of seconddilator 14 and is substantially flush with the outer surface of thesecond dilator 14. The second dilator 14 further includes a channel 46formed at or near the outer surface 42 of the closed side of seconddilator 14 extending the length of the second dilator 14 (FIG. 6) forreceiving an electrode in a manner to be described below. Because thebore of the second dilator 14 is offset toward the lobe 36 of the firstdilator, inserting the second dilator 14 over the first dilator 12causes the second dilator 14 to dilate the opening formed in the patientin a direction opposite the lobe 36 of the first dilator 12.

The third dilator 16 is characterized as being an open sided tubularstructure that has an outer surface 52, a proximal end 53, a distal end54 and a bore 55 extending from the proximal end 53 to the distal end54. The third dilator 16 is illustrated as having a substantiallycircularly shaped transverse cross section. The bore 54 is offset fromthe longitudinal axis of the third 16 dilator toward the open side ofthe third dilator 16. The bore 55 is shaped to slidingly receive thesecond dilator 12. As such, in the exemplary embodiment, the bore 55 isoval shaped. The third dilator 16 further includes a plurality ofchannels 56 formed at or near outer surface of the third dilator 14extending the length of the second dilator 14 (FIG. 6) for receivingelectrodes in a manner to be described below.

Because the bore 54 is oval shaped, the third dilator 16 may be insertedover the second dilator 14 in one of two ways. First, as illustrated inFIG. 5B, the third dilator 16 may be inserted over the second dilator 14with the open side of the third dilator 16 positioned opposite the openside of the second dilator 14. This causes the opening formed in thepatient by insertion of the third dilator 16 to be concentricallypositioned about the bore 35 of the first dilator 12. Second, asillustrated in FIG. 6, the third dilator 16 may be inserted over thesecond dilator 14 with the open side of the third dilator 16 positionedin alignment with the opposite the open side of the second dilator 14.This causes the opening formed in the patient by insertion of the thirddilator 16 to be eccentrically positioned about the bore 35 of the firstdilator 12 or in a direction away from the bore 35 of the first dilator12.

Referring again to FIGS. 1-3, the electrode assembly 18 includes anelectrode 60 and an electrode holder 62. The electrode 60 can be anyelectrode now or hereafter known for transmitting an electrical pulse.The electrode 60 includes an electrode tip 64 (FIG. 4B). The electrodeholder 62 is formed of an electrically insulating material and issubstantially similar in shape to the second dilator 14 so as to bepositionable about a portion of the first dilator 12. The electrode 60extends through the electrode holder 62 so that a proximal end of theelectrode 62 extends from an upper end of the electrode holder 62.

In use, the electrode holder 62 may function as a handle to facilitateinsertion of the electrode 60 into the channel 46 of the second dilator14 until the electrode holder 62 contacts the proximal end of the seconddilator 14 and the electrode tip 64 is position near the distal end 44of the second dilator 14 (FIG. 4B).

The electrode assembly 18 a includes three electrodes 70 and anelectrode holder 72. The electrodes 70 can be any electrode now orhereafter known for transmitting an electrical pulse. The electrodes 70include an electrode tip 74. The electrode holder 72 is substantiallysimilar in shape to the third dilator 14 so as to be positionable abouta portion of the second dilator 14. The electrodes extend through theelectrode holder 72 so that a proximal end of the electrodes 70 extendsfrom an upper end of the electrode holder 72.

In use, the electrode holder 72 may function as a handle to facilitateinsertion of the electrodes into the channels 56 of the third dilator 16until the electrode holder 72 contacts the proximal end of the thirddilator 16 and the electrode tips 74 are position near the distal end ofthe third dilator 16 (FIGS. 2, 3, and 4B).

The dilation system 10 is shown to use four electrodes to determinenerve location during the preparation of a surgical corridor. Fourelectrodes at final assembly allow nerves to be located 360° around thesurgical site without the additional step of rotating the dilators. Theassembly procedure would be carried out one dilator at a time with thefirst dilator 12 placed over a stimulating probe. Once the first dilator12 is in place, the probe may be removed and replaced with a K-wire, ifdesired. The second dilator 14 with a single disposable electrodeattached is placed over both the first dilator 12 and k-wire. The singleelectrode can be utilized to determine nerve proximity and the assemblycan be rotated as one unit. The third dilator 16 is placed over all theelements with three additional disposable electrodes attached. Oncefully assembled, the third and second dilators place the four electrodes90° apart allowing for nerve detection in four equally separateddirections spanning 360°.

Additionally, the eccentric dilators are shaped in an oblong fashion toprevent rotation between elements and allow for a unique assemblyorientation. The dilator assembly can be rotated at each step withoutcausing damage to surrounding tissue as a result of rotating interfacesand eliminates the possibility of single electrode misplacement relativeto the triple electrodes. This feature ensures that the four electrodesare placed 90° apart at final assembly and unwanted rotation betweendilators does not occur during use.

The shape of the dilators can be made so the dilators are assembled inan alternating pattern, which allows for the k-wire channel to belocated concentric to the final assembly. As well, the dilators can beassembled in an eccentric pattern, allowing for dilation to occur intissue in a single direction. This can be advantageous to performdilation in a direction away from nerve tissue.

Rotation between dilators can be eliminated via a keyhole slot, lockingmethod or other geometry. Greater or fewer dilatation steps can be used.Electrodes can be integrated into the dilators for greater than one timeuse. Electrodes can be placed in an alternative pattern. Electrodes canbe assembled in different combinations (e.g., two sets of twoelectrodes, four single electrodes, only two electrodes etc). Greater orfewer electrodes can be used. Dilator assembly could have a non-circularbasis.

Referring now to FIGS. 7-13, another embodiment of a dilation system 10a is illustrated. The dilation system 10 a includes a plurality ofsequential dilators 12 a, 14 a, and 16 a. The sequential dilation system10 a may include more or less dilators such as, for example, one, twofour, etc. The dilation system 10 a is adapted to be used in combinationwith a monitoring K-wire or stimulating probe (not shown) known fortransmitting an electrical pulse.

As best shown in FIGS. 11A and 11B, the first dilator 12 a ischaracterized as being an open sided tubular structure having an outersurface 32 a, a proximal end 33 a, a distal end 34 a, and a bore 35 aextending from the proximal end 33 a to the distal end 34 a. The firstdilator 12 a is illustrated as being substantially oval shaped. The bore35 a is offset from the longitudinal axis of the first dilator 12 a. Thebore 35 a is sized to receive a K-wire (not shown). The first dilator 12a is provided with an electrode 38 at the distal end 34 a generallyopposite the bore 35 a. The first dilator 12 a further has acorresponding connector point 39 (FIG. 11A) for connecting the electrodeto neural monitoring equipment.

As best shown in FIGS. 12A and 12B, the second dilator 14 a ischaracterized as being an open sided tubular structure having an outersurface 42 a, a proximal end 43 a, a distal end 44 a, and a bore 45 aextending from the proximal end 43 a to the distal end 44 a. The seconddilator 14 a is illustrated as having a substantially oval shapedtransverse cross section. The bore 45 a is offset from the longitudinalaxis of the second dilator 14 a toward the open side of the seconddilator 14 a. The bore 45 a is shaped to slidingly receive the firstdilator 12 a so that one side of the first dilator 12 a is received inthe open side of second dilator 14 a and is substantially flush with theouter surface of the second dilator 14 a. Alternatively, the seconddilator 14 a can be positioned over the first dilator 12 a with the opensides aligned. The second dilator 14 a is provided with an electrode 48at the distal end generally opposite the bore 45 a. The second dilator14 a further has a corresponding connector point 49 for connecting theelectrode to neural monitoring equipment.

Referring now to FIGS. 13A and 13B, the third dilator 16 a ischaracterized as being an open sided tubular structure that has an outersurface 52 a, a proximal end 53 a, a distal end 54 a, and a bore 55 aextending from the proximal end 53 a to the distal end 54 a. The thirddilator 16 a is illustrated as having a substantially circularly shapedtransverse cross section. The bore 55 a is offset from the longitudinalaxis of the third dilator 16 a toward the open side of the third dilator16 a. The bore 55 a is shaped to slidingly receive the second dilator 12a. As such, the bore is oval shaped. Because the bore is oval shaped,the third dilator 16 a may be inserted over the second dilator 14 a inone of two ways. First, as illustrated in FIG. 9, the third dilator 16 amay be inserted over the second dilator 14 a with the open side of thethird dilator 16 a positioned opposite the open side of the seconddilator 14 a. This causes the opening formed in the patient by insertionof the third dilator 16 a to be concentrically positioned about the boreof the first dilator 12 a. Second, as illustrated in FIG. 10, the thirddilator 16 a may be inserted over the second dilator 14 a with the openside of the third dilator 16 a positioned in alignment with the oppositethe open side of the second dilator 14 a. This causes the opening formedin the patient by insertion of the third dilator 16 a to beeccentrically positioned about the bore of the first dilator 12 a or ina direction away from the bore of the first dilator 12 a. The thirddilator 16 a is provided with an electrode 58 at the distal endgenerally opposite the bore 55 a. The third dilator 16 a further has acorresponding connector point 59 for connecting the electrode to neuralmonitoring equipment.

The electrodes of the first, second, and third dilators 12 a, 14 a, and16 a are provided for the purpose of determining the location of nervesor neural structures relative to the each of the dilators 12 a, 14 a,and 16 a as they are advanced over the K-wire towards or positioned ator near the surgical target site. The dilators 12 a, 14 a, and 16 a maybe equipped with the electrodes via any number of suitable methods,including but not limited to providing electrically conductive elementswithin the walls of the dilators such as by manufacturing the dilatorsfrom plastic or similar material capable of injection molding ormanufacturing the dilators from aluminum (or similar metallic substance)and providing outer insulation layer with exposed regions (such as byanodizing the exterior of the aluminium dilator).

As best shown in FIGS. 3 and 7, the first dilators 12 and 12 a have alength greater than the length of the second dilator 14 and 14 a,respectively, and the second dilators 14 and 14 a have a length greaterthan the length of the third dilators 16 and 16 a, respectively. Thisstepped arrangement permits the proximal ends of the first dilators 12and 12 a to extend further out of the patient in the assembled andoperational configurations to facilitate connection of the electrodes tothe neural monitoring equipment and such that a surgeon may grasp andremove or otherwise manipulate the dilators.

It should be understood that the dilators described above may include aplurality of depth indicators located on the outer surface thereof.

A method of using the dilation systems 10 and 10 a will now be describedfor accessing a patient's spine. The technique may be particularlydesirable for accessing the lumbar region of the spine via a lateralapproach, although a similar or the same method may be used in otherparts of the patient's body.

Using a stimulating probe and an electromyograph (EMG) (not shown) in amanner similar to that described in U.S. 2011/0208226, which is herebyexpressly incorporated herein by reference, the surgeon may map a safezone, i.e., a zone generally free of any neural elements or nerves, onthe tissue of interest (e.g., psoas muscle). For example, on the psoasmuscle, the anterior third of the psoas muscle is generally considered asafe zone.

Once a safe zone is established, anatomical placement may be confirmedvia intra-operative fluoroscopy. The surgeon inserts the stimulatingprobe through the psoas muscle toward the patient's spine. If thesurgery is being performed on the intervertebral disc space, the distalend of the stimulating probe may be inserted into the annulus of thedesired intervertebral disc space. The stimulating probe may be insertedvia the most posterior portion of the safe zone.

The surgeon can insert or slide the first dilator 12, 12 a over thestimulating probe so that the first longitudinal axis is located to oneside of the stimulating probe, away from a sensed neural element ornerve, through the psoas muscle and into a position proximate thepatient's spine. The surgeon can then insert the second dilator 14, 14a, if necessary, to further dilate the tissue proximate the outsidesurface of the first dilator 12, 12 a and in a desired direction. Thesurgeon can repeat this process as often as necessary. Finally, ifdesired, a retractor (not shown) can be inserted over the third dilator16, 16 a to subsequently retract the tissue and to permit removal of thedilation system 10, 10 a and the stimulating probe.

Referring now to FIG. 14, another embodiment of a dilation system 100 isillustrated. The dilation system 100 includes a plurality of sequentialdilators 112, 114, and 116. The dilation system 100 may include more orless dilators such as, for example, one, two four, etc. The dilationsystem 100 is adapted to be used in combination with a monitoring K-wireor stimulating probe 118 known for transmitting an electrical pulse.

Referring now to FIGS. 15A, 16A-16D, 17, and 18, the first dilator 112is an elongated, tubular member having an outer surface 120, a proximalend 122, a distal end 124 and a bore 126 extending from the proximal end122 to the distal end 124. The bore 126 is sized to receive thestimulating probe 118. The first dilator 112 may be provided with asecond bore or channel 138 extending parallel to the bore 126 and thelength of the first dilator 112 for receiving an electrode 140.

The first dilator 112 is further characterized as having a lower section128, an upper section 130, and an intermediate section 132. The lowersection 128 is sized and configured to be extended through the psoasmuscle. By way of example, the lower section 128 may have a diameter ina range of from about 4 mm to about 10 mm. In one embodiment, the lowersection 128 has a generally keyhole shaped cross section.

The upper section 130 of the first dilator 112 is provided with a firstguide 134 and a second guide 136 which are configured to slidably andmatingly engage with the second dilator 114 and the third dilator 116,respectively, in a manner to be discussed below. The first guide 134 isillustrated has having a dovetail configuration with a taper at aproximal end thereof to facilitate engagement with the second dilator114. Similarly, the second guide 136 is illustrated as having a dovetailconfiguration with a taper at a proximal end thereof to facilitateengagement with the third dilator 116. In one embodiment, the firstguide 134 and the second guide 136 extend radially outwardly indiametrically opposing directions.

It should be appreciated that the first guide 134 and the second guide136 may be formed in a variety of shapes. For example, the first guide134 and the second guide 136 may be formed as grooves configured toreceive a dovetail tongue. Also, the first guide and the second guidemay be formed so that the size of the first guide 134 is different fromthe size of the second guide 136 for reasons that will be describedbelow.

The intermediate section of the first dilator 112 may be an open sidedstructure, and shaped similar to the lower section 128 (e.g., generallykeyhole shaped cross section). As illustrated in FIG. 16D, the firstdilator 112 may be constructed in multiple pieces. For example, thelower section 128, the upper section 130, and the intermediate section132 may be formed as separate pieces which are adapted to be assembledwith one another. It will also be understood that the first dilator 112may be formed as a single piece.

With reference to FIGS. 15B, 19, 20A, and 20B, the second dilator 114 isconfigured to slide along the first dilator 112 (FIG. 15B) and bepositioned to create a semi-circular cross section that assists withslitting muscle fibers when a combination of the first dilator 112 andthe second dilator 114 are rotated about the stimulated probe 118. Thesecond dilator 114 is generally characterized as being an elongated,open sided or C-shaped structure that has an outer surface 141, an innersurface 142, a proximal end 143, a distal end 144, and a bore 145extending from the proximal end 143 to the distal end 144 for receivingan electrode, such as the electrode 140, in a manner to be describedbelow.

The second dilator 114 is further characterized as having a lowersection 146, an upper section 148, and an intermediate section 150. Theinner surface 142 of the lower section 146 is sized and configured to bematingly received over a corresponding portion of the lower section 128of the first dilator 112. The inner surface 142 of the upper section 148of the second dilator 114 is configured to slidably and matingly engagewith the first guide of the first dilator 112. To this end, the uppersection 148 of the second dilator 114 has a groove 152 corresponding tothe shape of the first guide 134. Again, it will be appreciated that thefirst guide 134 and the groove 152 may be formed in a variety of shapesand that the position of the first guide 134 and the groove mayinterchanged. To facilitate sliding of the second dilator 114 over thefirst dilator 112, the inner surface 142 of the intermediate section 150of the second dilator 114 may be configured so that the inner surface142 is in a non-contact relationship with the outer surface 120 of thefirst dilator 112.

The second dilator 114 has a first longitudinal edge 154 and a secondlongitudinal edge 156. The bore 145 may be formed proximate to the firstlongitudinal edge 154. The second longitudinal edge 156 may be angled toform a wedge with the inner surface 142 of the second dilator 114 tofacilitate rotation of the first dilator 112 and the second dilator 114relative to the muscle fiber.

With reference to FIGS. 15C, 21, 22A, 22B, the third dilator 116 isconfigured to slide along the first dilator 112 and be positioned totransform the semi-circular cross section of the combination of thefirst dilator 112 and the second dilator 114 to a circular cross sectionof a selected diameter, e.g. 16 mm-22 mm. The third dilator 116 isgenerally characterized as being an elongated, open sided or C-shapedstructure that has an outer surface 160, an inner surface 162, aproximal end 164, a distal end 166 and a bore 168 extending from theproximal end 164 to the distal end 166 for receiving an electrode, suchas the electrode 140, in a manner to be described below.

The third dilator 116 is further characterized as having a lower section170, an upper section 172, and an intermediate section 174. The innersurface 162 of the lower section 172 is sized and configured to bematingly received over a corresponding portion of the lower section 128of the first dilator 112. The inner surface 162 of the upper section 174of the third dilator 116 is configured to slidably and matingly engagewith the second guide 136 of the first dilator 112. To this end, theupper section 174 of the third dilator 116 has a groove 176corresponding to the shape of the second guide 136. Again, it will beappreciated that the second guide 136 and the groove 176 may be formedin a variety of shapes and that the position of the second guide 136 andthe groove 176 may be interchanged. To facilitate positioning of thethird dilator 116 over the first dilator 112, the inner surface 162 ofthe intermediate section 176 of the third dilator 116 may be configuredso that the inner surface 162 is in a non-contact relationship with theouter surface 120 of the first dilator 112.

The third dilator 116 has a first longitudinal edge 178 and a secondlongitudinal edge 180. The bore 168 may be formed proximate to the firstlongitudinal edge 178. The first longitudinal edge 178 and the secondlongitudinal edge 180 of the third dilator 116 are configured to matewith the second longitudinal edge 156 and the first longitudinal edge154 of the second dilator 114, respectively. Because the firstlongitudinal edge 154 and the second longitudinal edge 156 of the seconddilator 114 are angled to facilitate rotation within the psoas muscle,the first longitudinal edge 178 and the second longitudinal edge 180 ofthe third dilator 116 have an inverse shape to that of the firstlongitudinal edge 154 and the second longitudinal edge 156 of the seconddilator 114 so as to mate with the first and second longitudinal edges154 and 156 of the second dilator 114. To facilitate insertion of thesecond dilator 114 on the first dilator 112 prior to insertion of thethird dilator 116, the first guide 134 and the second guide 136 may besized differently from one another and the grooves 152 and 176 of thesecond and third dilators 114 and 116 may be sized to mate with thecorresponding one of the first and second guides 134 and 136.

A method of using the dilation systems 100 will now be described foraccessing a patient's spine. The technique may be particularly desirablefor accessing the lumbar region of the spine via a lateral approach,although a similar or the same method may be used in other parts of thepatient's body.

Using a stimulating probe 118 and an electromyograph (EMG) (not shown),a surgeon may map a safe zone, i.e., a zone generally free of any neuralelements or nerves, on the tissue of interest (e.g., psoas muscle). Forexample, on the psoas muscle, the anterior third of the psoas muscle isgenerally considered a safe zone.

Once a safe zone is established, anatomical placement may be confirmedvia intra-operative fluoroscopy. The surgeon inserts the stimulatingprobe 118 through the psoas muscle toward the patient's spine. If thesurgery is being performed on the intervertebral disc space, the distalend of the stimulating probe 118 may be inserted into the annulus of thedesired intervertebral disc space. The stimulating probe 118 may beinserted via the most posterior portion of the safe zone.

The surgeon can insert or slide the first dilator 112 over thestimulating probe 118, through the psoas muscle, and into a positionproximate the patient's spine. The surgeon can insert a stimulatingprobe 140 into the bore 138 so that a surgeon can stimulate the firstdilator 112 while the first dilator 112 is being inserted into position.The surgeon can then insert the second dilator 114 on the first dilator112 by inserting the second dilator 114 laterally into to engagementwith the first dilator 112 with the upper section of the second dilator114 positioned above the first guide 134 of the first dilator 112 (FIG.15B).

The second dilator 114 may then be slid downwardly along the firstdilator 112 in such a way that the groove 152 of the second dilator 114is received over the first guide 134 of the first dilator 112 so as toaxially guide the second dilator 114 through the psoas muscle andfurther dilate the tissue. Prior to positioning the second dilator 114,the surgeon can remove the electrode 140 from the first dilator 112 andinsert the electrode 140 into the bore 143 of the second dilator 114 tostimulate the second dilator 114 while the second dilator 114 is beinginserted into position. The surgeon can repeat this process using thethird dilator 116. Finally, if desired, a retractor can be inserted overthe second dilator 114 and the third dilator 116 to subsequently retractthe tissue and to permit removal of the dilation system 100 and thestimulating probe 118 and the electrode 140.

Referring now to FIGS. 23A-23C, another embodiment of a dilation system200 is illustrated. The dilation system 200 includes a pair of dilators202 and 204. The dilation system 200 may include more or less dilatorssuch as, for example, one, three four, etc. The dilation system 200 isadapted to be used in combination with a monitoring K-wire orstimulating probe (not shown) known for transmitting an electricalpulse.

Referring now to FIG. 23A, the first dilator 112 is an elongated memberhaving an outer surface 206, a proximal end 208, a distal end 210, and abore 212 extending from the proximal end 208 to the distal end 210. Thebore 212 is sized to receive a K-wire or stimulating probe, such as thestimulating probe 118 illustrated in FIG. 14. The first dilator 202 canbe manufactured such that the K-wire can be accommodated via acontinuous thru-bore or an open slot located closer to the outer surfaceof the first dilator 202.

The first dilator 202 is used to create the initial access corridor. Thedistal end 210 is tapered to facilitate insertion into tissue, and thedistal end 212 is stimulatable via an exposed electrode 214. The generalshape of the first dilator 202 is atraumatic. A connector 216 isprovided along one side of the first dilator 202. The connector 216 isillustrated as being a dovetail groove.

In use, the first dilator 202 is inserted over the K-wire or stimulatingprobe with the connector 216 positioned in an anterior direction tomonitor the proximity of nerves.

The second dilator 204 is used to further dilate tissue and can beadvanced into position directly anterior to the first dilator 202. Thesecond dilator 204 is an elongated member having an outer surface 220, aproximal end 222, and a distal end 224. Like the first dilator 202, thesecond dilator 204 may be manufactured with a stimulatable electrode.The shape of the second dilator 204 is atraumatic as it passes throughtissue. The second dilator 204 is configured to connect to and slidealong the length of the first dilator 202. To this end, the seconddilator 204 has a connector 226. The connector 226 of the second dilator204 is configured for sliding and mating engagement with the connector216 of the first dilator 202. In one embodiment, the connector 226 is adovetail tongue that allows for the second dilator 204 to slide alongthe length of the first dilator 202 while maintaining attachment.

The dilation system 200 further includes a retractor blade assembly 230(FIG. 23C) which is shown to include three blades 232 a, 232 b, and 232c. The contour of the blades 232 a, 232 b, and 232 c, when assembled,closely matches the outer profile of a combination of the first dilator202 and the second dilator 204. The posterior retractor blade 232 a mayhave an embedded electrode and accompanying wiring to enable monitoringof nerves. The electrode and wiring can be embedded into the dilatorblades and retractor blades or added afterwards by a sticky probe orconductive epoxy ink.

The dilators and the retractor blades can be machined, molded, orextruded and machined from materials such as stainless steel, anodizedaluminum, PEEK, carbon fiber composite, or any biocompatible materialsuitable to maintain the shape and function of the components.

FIGS. 24-28 illustrate another embodiment of a dilation system 300constructed in accordance with the inventive concepts disclosed herein.The dilation system 300 is used to create an initial corridor which maybe expanded to a desired diameter, e.g., 16-22 mm, without inserting anyadditional instruments. In addition, the dilation system 300 is adaptedto be used with a k-wire or stimulating probe, such as the stimulatingprobe 118 illustrated in FIG. 14. The dilation system 300 includes abase 302, a first blade 304, a second blade 306, and an actuatingmechanism 308 operably associated with the first blade 304 and thesecond blade 306 so as to cause the first blade 304 and the second blade306 to move from a closed condition (FIG. 24A) wherein the first blade304 and the second blade 306 are positioned adjacent one another topermit insertion through selected tissue to an expanded condition (FIG.24B) wherein the first blade 304 and the second blade 306 are spreadapart relative to one another to expand the tissue.

The first blade 304 has a proximal end 310 and a distal end 312. Thefirst blade 304 extends from the base 302 so that the distal end 312 ofthe first blade 304 extends away from the base 302 in such a way thatthe distal end 312 is deflectable relative to the proximal end 310.Similarly, the second blade 306 has a proximal end 314 and a distal end316. The second blade 306 extends from the base 302 so that the distalend 316 of the second blade 306 extends away from the base 302 in such away that the distal end 316 is deflectable relative to the proximal end314. Each of the first blade 304 and the second blade 306 has agenerally arcuate cross section and the distal ends 312 and 316 may betapered to facilitate insertion into a patient. Each of the first blade304 and the second blade 306 may be provided with a bore or channel (notshown) extending the length of the first dilator 112 for receiving anelectrode (not shown) to aid in stimulating adjacent tissues.

The actuating mechanism 308 includes a linkage 320, a drive rod 322, anda drive member 324. In one embodiment, the linkage 320 includes a pairof cross links 326. Each cross link 326 is identical in construction andhas a body 328 with a pin 330 pivotally connectable to the distal ends312 and 316 of the first blade 304 and the second blade 306 via a groove331 formed in the distal ends 312 and 316 of the first blade 304 and thesecond blade 306. Each cross link 326 further includes a pin 332 andhole 334 with the pin 332 being received through the hole 334 of theother cross link 326 and the hole 334 receiving the pin 332 of the othercross link 326. The body 328 is provided with a longitudinal groove 336for receiving a stimulating probe when the first blade 304 and thesecond blade 306 are in the closed condition.

The drive rod 322 has a proximal end 338 and a distal end 340, and thedrive rod 322 is positioned between the first blade 304 and the secondblade 306. The distal end 340 of the drive rod 322 is provided with pairof holes 342 for pivotally receiving the pins 332 of the cross links 326such that axial movement of the drive rod 322 moves the first blade 304and the second blade 306 from the closed condition to the expandedcondition.

The drive member 324 is rotatably connected to the base 302, and theproximal end 338 of the drive rod 322 is threadingly connected to thedrive member 324 in such a way that rotational movement of the drivemember 324 causes axial movement to the drive rod 322.

The drive member 324 and the drive rod 322 have a central bore 344 sizedto receive a stimulating probe. Further, the distal end 312 of the firstblade 304 may have a first notch 346, and the distal end 316 of thesecond blade 306 may have a second notch 348. The first notch 346 andthe second notch 348 are aligned to cooperate to form an opening 350(FIG. 24A) sized to receive the stimulating probe when the first blade304 and the second blade 306 are in the closed condition.

Referring to FIGS. 28A and 28B, the dilation system 300 may furtherinclude an expandable sheath 352 positioned about at least the distalends of the first blade 304 and the second blade 306 to cover the spacesbetween the first blade 304 and the second blade 306. The sheath 352 canbe made of any type of expandable material, such as a mesh, fabric,polymer, or elastomeric polymer.

Referring now to FIGS. 29-33, another embodiment of a dilation system400 is illustrated. The dilation system 400 is used to create an initialcorridor which may be expanded to a desired diameter, e.g., 16-22 mm,without inserting any additional instruments. In addition, the dilationsystem 400 is adapted to be used with a k-wire or stimulating probe,such as the stimulating probe 401. The dilation system 400 includes abase 402, a first blade 404, a second blade 406, and an actuatingmechanism 408 operably associated with the first blade 404 and thesecond blade 406 so as to cause the first blade 404 and the second blade406 to move from a closed condition (FIG. 29) wherein the first blade404 and the second blade 406 are positioned adjacent one another adistance to permit insertion through selected tissue to an expandedcondition (FIGS. 30 and 31) wherein the first blade 404 and the secondblade 406 are spread apart relative to one another a selected distanceto expand the tissue.

The first blade 404 has a proximal end 410 and a distal end 412. Thefirst blade 404 extends from the base 402 so that the distal end 412 ofthe first blade 404 extends away from the base 402 in such a way thatthe distal end 412 is deflectable relative to the proximal end 410.Similarly, the second blade 406 has a proximal end 414 and a distal end416. The second blade 406 extends from the base 402 so that the distalend 416 of the second blade 406 extends away from the base 402 in such away that the distal end 416 is deflectable relative to the proximal end414. Each of the first blade 404 and the second blade 406 has agenerally arcuate cross section and the distal ends 412 and 416 may betapered to facilitate insertion into a patient. Each of the first blade404 and the second blade 406 may be provided with a bore or channel (notshown) extending the length thereof for receiving an electrode (notshown) to aid in stimulating adjacent tissues.

As best illustrated in FIGS. 32 and 33, the actuating mechanism 408includes a drive rod 418, an expander member 420, a guide 422, and asecond expander member 423 (FIG. 33). The drive rod 418 has a proximalend 424 and a distal end 426. The drive rod 418 extends between thefirst blade 404 and the second blade 406 and is rotatably connected tothe base 402 in such a way that the drive rod 418 is rotatable throughan angle of at least about 90 degrees. In one embodiment, the base 402is provided with a pair of diametrically opposed slots 428 (only oneslot 428 being visible), and the guide rod 418 is provided with a pairof diametrically opposed pins 430 extending radially therefrom andslidably received in the slots 428. The drive rod 418 has a central bore431 sized to receive the stimulating probe 401.

The expander member 420 extends from the drive rod 418 in such a waythat rotational movement of the drive rod 418 moves the first blade 404and the second blade 406 from the closed condition to the expandedcondition. As best illustrated in FIG. 32, the expander member 420 mayinclude a pair of flanges or protrusions 432 that are sized and shapedto contact the first blade 404 and the second blade 406 and move thefirst blade 404 and the second blade 406 to the expanded condition uponrotation of the drive rod 418. The guide member 422 may extend from thedrive rod 418 in a substantially perpendicular relationship of theexpander member 420 for guiding the second expander member 423 in amanner to be discussed below.

The second expander member 423 is slidably positionable over the driverod 418 and between the first blade 404 and the second blade 406 so asto extend between the first blade 404 and the second blade 406 to fillthe gap between the longitudinal edges of the first blade 404 and thelongitudinal edges of the second blade 406. The second expander 423 mayinclude a base 434, a first blade 436 extending from the base 434, and asecond blade 438 extending from the base 434 in a spaced apart, parallelrelationship to the first blade 436 so that the first blade 436 and thesecond blade 438 are slidably positionable over the expander member 420when the expander member 420 is rotated to the expanded condition. Thefirst blade 436 and the second blade 438 may be provided with a slot 440extending along at least a portion an inner surface thereof forslidingly receiving a portion of the guide member 422.

Each of the first blade 436 and the second blade 438 has a generallyarcuate cross section and the distal ends may be provided with a raisedarea 442 which is positionable substantially flush with the outersurfaces of the first blade 404 and the second blade 406 in the expandedcondition so that the first blade 436 and the second blade 438 cooperatewith the first blade 404 and the second blade 406 to form a circularcross section of a selected diameter, e.g. 16 mm-22 mm.

As an alternative to use of the second expander 423 to fill the gapsbetween the first blade 404 and the second blade 406, it will beappreciated that the dilation system 400 may further include anexpandable sheath positioned about at least the distal ends of the firstblade 404 and the second blade 406 to cover the spaces between the firstblade 404 and the second blade 406. As described above, the sheath canbe made of any type of expandable material, such as a mesh, fabric,polymer, or elastomeric polymer.

FIGS. 34 and 35 illustrate another embodiment of a dilation system 500constructed in accordance with the inventive concepts disclosed herein.The dilation system 500 is used to create an initial corridor which maybe expanded to a desired diameter, e.g., 16-22 mm, without inserting anyadditional instruments. In addition, the dilation system 500 is adaptedto be used with a k-wire or stimulating probe, such as a stimulatingprobe 501. The dilation system 500 includes a base 502, a first blade504, a second blade 506, and an actuating mechanism 508 operablyassociated with the first blade 504 and the second blade 506 so as tocause the first blade 504 and the second blade 506 to move from a closedcondition wherein the first blade 504 and the second blade 506 arepositioned adjacent one another a distance to permit insertion throughselected tissue to an expanded condition (FIGS. 34 and 35) wherein thefirst blade 504 and the second blade 506 are spread apart relative toone another a selected distance to expand the tissue.

The first blade 504 has a proximal end 510 and a distal end 512. Thefirst blade 504 extends from the base 502 so that the distal end 512 ofthe first blade 504 extends away from the base 502 in such a way thatthe distal end 512 is deflectable relative to the proximal end 510.Similarly, the second blade 506 has a proximal end 514 and a distal end516. The second blade 506 extends from the base 502 so that the distalend 516 of the second blade 506 extends away from the base 502 in such away that the distal end 516 is deflectable relative to the proximal end514. Each of the first blade 504 and the second blade 506 has agenerally arcuate cross section and the distal ends 512 and 516 may betapered to facilitate insertion into a patient. Each of the first blade504 and the second blade 506 may be provided with a bore or channel (notshown) extending the length thereof for receiving an electrode (notshown) to aid in stimulating adjacent tissues.

The actuating mechanism 508 includes a drive rod 518 having a proximalend and a distal end. The drive rod is positioned between the firstblade 504 and the second blade 506 and configured in such a way thataxial movement of the drive rod 518 moves the first blade 504 and thesecond blade 506 from the closed condition to the expanded condition.The drive rod 518 may have a wedge shape so that axial movement of thedrive rod 518 wedge will drive the first blade 504 and the second blade506 in a radial direction to larger or smaller diameters.

The drive rod 518 may be moved in a variety of different ways. Forexample, the drive rod 518 may be axially moved manually by sliding thedrive rod 518 between the first blade 504 and the second blade 506.Also, the drive rod 518 may be moved in a manner similar to thatdescribed above with respect to the dilation system 200 where the driverod 518 may be moved with an internally threaded assembly, by way ofexample.

The expansion of the first blade 504 and the second blade 506 will leavegaps as they go to the large circumferences so these gaps should becovered to effectively dilate the tissue. To this end, the dilationsystem 500 may include an expandable sheath 520 (FIG. 35) positionedabout at least the distal ends of the first blade 504 and the secondblade 506 to cover the spaces between the first blade 504 and the secondblade 506. The sheath 520 may be laterally supported by a plurality ofsupport member 522 (only one support member 522 being visible in FIG.35). As described above, the sheath 520 can be made of any type ofexpandable material, such as a mesh, fabric, polymer, or elastomericpolymer. The sheath 520 may alternatively be in the form of a pluralityof metal slotted tubes connected to the blades 504 and 506. The slottedtubes must be made out of an elastic material such as nitinol toaccommodate the bending to a larger diameter. The tubes are initiallynested within each other. As the blades are driven radially outward theyinteract with each other such that the diameters of tubing willincrease. The sliding and expanding action will maintain an enclosedcylinder with some discontinuities, but no gaps. Alternatively, thedrive rod 518 may be configured to file in the gaps.

Referring now to FIGS. 36-38, another embodiment of a dilation system600 is illustrated. The dilation system 600 includes a first dilator601, an expandable dilator 602, and a plurality of expansion dilators604 positionable between the first dilator 601 and the expandabledilator 602 to enlarge the surgical corridor and create an enlargedworking space. The first dilator 601 is a generally tubular member witha bore 606 for receiving a K-wire or stimulating probe, such as thestimulating probe 118 of FIG. 14.

The expandable dilator 602 includes an expandable sheath 608 and aplurality of support members 610 extending longitudinally along an innersurface of the sheath 608 in a spaced apart relationship to providelongitudinal support to the sheath 608 while allowing for the sheath 608to expand radially. The sheath 608 may be constructed of any suitableelastomeric material. The support members 610 are sized to extend alongthe length of the sheath 608 may be connected to sheath 602 in anysuitable manner, such as use of an adhesive, weaving the support arms inthe sheath 602, or embedding the support members 610 in the sheath 608,for example. While the expandable dilator 602 is shown as having foursupport members 608, it will be appreciated that the expandable dilator602 may expand with the use of at least three support members 610.However, the sheath 608 will created a rounder corridor the more supportmembers 610 that are utilized.

In use, the first dilator 601 is inserted through tissue up to a discannulus while monitoring neural structures. A K-wire may be insertedthrough the bore 606 of the first dilator 601 to dock the first dilator601 to a disc annulus. The expandable dilator 602 is then inserted overthe first dilator 601 as shown in FIGS. 36A and 36B. A second dilator604 a (FIGS. 37A and 37B) may then be inserted between first dilator 601and the expandable dilator 602, thereby expanding the sheath 608. Asshown in FIGS. 38A and 38C, a third dilator 604 b may be insertedbetween the second dilator 604 a and the expandable dilator 602, therebyfurther expanding the sheath 608. A retractor (not shown) may beinserted about the sheath 608, and the dilation system 600 and theK-wire removed.

As shown, the support members 610 and the dilators 601, 604 a and 604 bmay be provided with corresponding tongues 612 and grooves 614 foraligning the dilators to one another during expansion. The tongue andgroove construction also allows the sheath 608 to expand uniformly. Thedilation system 600 has an advantage in that only two dilators areinserted that pass through tissue which minimizes tissue trauma as theremaining dilators are used to expand the dilation system radiallywithout any further insertion forces. This is due to the sheathremaining in contact with tissue for the remainder of the expansion.

Electrodes, such as electrode 616, may be embedded in or on the firstdilator 601 and the sheath 608 to allow for surrounding neural tissue tobe identified, monitored, and assessed based on distance and pathology.

From the above description, it is clear that the inventive conceptsdisclosed and claimed herein are well adapted to carry out the objectsand to attain the advantages mentioned herein, as well as those inherentin the invention. While exemplary embodiments of the inventive conceptshave been described for purposes of this disclosure, it will beunderstood that numerous changes may be made which will readily suggestthemselves to those skilled in the art and which are accomplished withinthe spirit of the inventive concepts disclosed and claimed herein.

1. A dilation system, comprising: a first dilator having an outersurface, a proximal end, a distal end, and a bore extending from theproximal end to the distal end, the first dilator having a substantiallyegg shaped transverse cross section so as to define a lobe, the borebeing offset from the longitudinal axis of the first dilator away fromlobe, the bore sized to receive a stimulating probe; and a seconddilator having an outer surface, a proximal end, a distal end, and abore extending from the proximal end to the distal end, the seconddilator having a substantially oval shaped transverse cross section, thebore being offset from the longitudinal axis of the second dilator andshaped to slidingly receive the first dilator.
 2. The dilation system ofclaim 1 or 2, wherein the bore of the second dilator is offset towardthe open side of the second dilator.
 3. The dilation system of any oneof claims 1-3, wherein the second dilator is an open sided tubularstructure and wherein the bore of the second dilator is shaped toslidingly receive the first dilator so that the tip of the lobe of thefirst dilator is received in the open side of second dilator and issubstantially flush with the outer surface of the second dilator.
 4. Thedilation system of claim 1, wherein the second dilator further includesa channel formed at or near the outer surface of the closed side ofsecond dilator extending the length of the second dilator for receivingan electrode.
 5. The dilation system of any one of claims 1-4, furthercomprising: a third dilator having an outer surface, a proximal end, adistal end, and a bore extending from the proximal end to the distalend, the third dilator having a substantially circularly shapedtransverse cross section, the bore being offset from the longitudinalaxis of the third dilator toward the open side of the third dilator, andshaped to slidingly receive the second dilator.
 6. The dilation systemof any one of claims 1-5, wherein the third dilator is an open sidedtubular structure and wherein the bore of the third dilator is shaped toslidingly receive the second dilator so that the tip of the lobe of thefirst dilator is received in the open side of second dilator and issubstantially flush with the outer surface of the second dilator.
 7. Thedilation system of any one of claims 1-6, wherein the third dilatorfurther includes a plurality of channels formed at or near outer surfaceof the third dilator extending the length of the third dilator forreceiving electrodes.
 8. The dilation system of any one of claims 1-7,wherein the third dilator slidingly receives the second dilator with theopen side of the third dilator positioned opposite the open side of thesecond dilator in such a way that causes the opening formed in thepatient by insertion of the third dilator to be concentricallypositioned about the bore of the first dilator.
 9. The dilation systemof any one of claims 1-7, wherein the third dilator slidingly receivesthe second dilator with the open side of the third dilator positioned inalignment with the open side of the second dilator in such a way thatcauses the opening formed in the patient by insertion of the thirddilator to be eccentrically positioned about the bore of the firstdilator or in a direction away from the bore of the first dilator.
 10. Adilation system, comprising: a first dilator having an outer surface, aproximal end, a distal end, and a bore extending from the proximal endto the distal end, the first dilator having a first guide and a secondguide formed on the proximal end thereof, the bore sized to receive astimulating probe; a second dilator having an outer surface, a proximalend, a distal end, and a bore extending from the proximal end to thedistal end, the second dilator having a generally C-shaped transversecross section, the proximal end of the second dilator configured toslidably mate with the first guide of the first dilator; and a thirddilator having an outer surface, a proximal end, a distal end, and abore extending from the proximal end to the distal end, the thirddilator having a generally C-shaped transverse cross section, theproximal end of the third dilator configured to slidably mate with thesecond guide of the first dilator.
 11. The dilation system of claim 10,wherein the first guide has a first size, wherein the second guide has asecond size, and wherein the first size is different from the secondsize.
 12. The dilation system of any one of claim 10 or 11, wherein thefirst guide and the second guide extend radially outwardly in opposingdirections.
 13. The dilation system of any one of claims 10-12, whereineach of the first guide and the second guide has a tapered proximal end.14. The dilation system of any one of claims 10-13, wherein the seconddilator has a first longitudinal edge and a second longitudinal edge,wherein the third dilator has a first longitudinal edge and a secondlongitudinal edge, and wherein the first longitudinal edge of the seconddilator and the second longitudinal edge of the third dilator areconfigured to mate with one another and the second longitudinal edge ofthe second dilator and the first longitudinal edge of the third dilatorare configured to mate with one another when the second dilator and thethird dilator are positioned on the first dilator.
 15. The dilationsystem of claim 14, wherein the configuration of the first longitudinaledge of the second dilator is different than the configuration of thesecond longitudinal edge of the second dilator.
 16. The dilation systemof any one of claims 10-15, wherein the second dilator further includesa channel formed at or near the outer surface thereof extending thelength of the second dilator for receiving an electrode.
 17. Thedilation system of any one of claims 10-16, wherein the third dilatorfurther includes a channel formed at or near the outer surface thereofextending the length of the third dilator for receiving an electrode.18. The dilation system of any one of claims 10-17, wherein the firstdilator has a proximal portion, a distal portion, and a medial portion,at least a portion of the medial portion having a longitudinal slot fromthe outer surface and intersecting the bore of the first dilator in sucha way that a portion of the bore of the first dilator is open sided. 19.The dilation system of any one of claims 10-18, wherein the bore of thefirst dilator defines a first bore, and wherein the first dilatorfurther has a second bore extending from the proximal end to the distalend in a parallel relationship with the first bore, the second boresized to receive a stimulating probe.
 20. The dilation system of claim19, wherein the first bore and the second bore of the first dilator havea common open side along the length of the first bore and the secondbore. 21-44. (canceled)